Solvation process for carbonaceous fuels



Sept. 12, 1967 w. c. BULL ETAL 3,341,447 SOLVATION PROCESS FOR CARBONACEOUS FUELS Filed Jan. 18, 1965 COAL DEASHING PROCESS SCHEMATIC FLOW DIAGRAM MAKE-UP COAL FEED SOLVENT SOLVENT RECOVERED SLURRY V NT TANK E LIGHT OIL FEED PUMP MAKE-UP ,.VENT 8 f3 RECYCLE GAS DISTILLATION PRE- CAUSTIC HEATER 6 GAS "1 TREATMENT olscHAggE FgR S H28 H2 FURTH R c 5 INS DISSOLVER 4 CO2 CH4 (H28 & CO2) co CzHs I N2 LIGHT OIL 7 EVAPORATOR SOLIDIFICATION BELT :[I ASH RESIDUE E PRODUCT FILTER CAKE PROCESSING INVENTOR'S Willard C. Bull Lawrence G. Stevenson Dean L. Klaepper Thomas F. Rogers United States Patent 6 3,341,447 SOLVATION PROCESS non cARBoNAcEoUs UELs This invention relates to the solubilizing of carbonaceous fuels, and more particularly to the upgrading of carbonaceous fuels by a solution-process into low-ash low-oxygen, low-sulfur fuels.

This invention resulted from work done under Contract 14-01-0001-275 with the Ofiice of Coal Research in the Department of the Interior entered into pursuant to the Coal Research Act, 30 U.S.C. 661 to 668.

Processes for the extraction of carbonaceous fuels, such as bituminous and subbituminous coals, lignites, peat and the like, by solvents under a hydrogen atmosphere are known. However, because of the economics of these known processes, they have necessarily been limited and restricted for the preparation of highly specialized products such as waxes and other low volume, high priced materials. The economics of these old processes have prevented their use for the upgrading of carbonaceous fuels into gasoline, diesel oil, lubricating oils, kerosene and other refined solid fuels because of various reasons. The basic reason for the failure to commercially utilize these processes for the upgrading of carbonaceous fuels is that the processing costs of these old processes are too prohibitive to enable the product to be competitive with alternate low cost fuels, as for example residual oil from petroleum. Two of the prime factors making the cost of such processes prohibitive are the inability to obtain complete solubilization of all of the potentially available carbonaceous fuel used as fuel for the process and the inability to recycle solvent to the system without special treatment. As a further factor, those old processes require excessive amounts of hydrogen.

In contrast to the foregoing the present invention has for one of its objects to provide a novel process for essentially complete solubilization of carbonaceous fuels in solvent.

Another object of this invention is to provide a novel and economical process for preparing low-ash, lowoxygen, low-sulfur fuels from naturally occurring carbonaceous fuels.

A further object of this invention is to provide a novel, economical and improved process for the solubilization of naturally occurring carbonaceous fuels for the upgrading thereof into solid low-ash, low-oxygen, low-sulfur fuels which are commercially competitive with other fuels.

A still further object of this invention is to provide a novel and improved process for the production of solid low-ash, low-oxygen, low-sulfur fuels from carbonaceous fuels, which process is cyclic and does not require any substantial addition of solvent after start-up.

A still further object of this invention is to provide a novel process for the upgrading of naturally occurring carbonaceous fuels into novel low-ash, low-oxygen, lowsulfur fuels.

A still further object of this invention is to prepare commercially competitive solid low-ash, low-oxygen, lowsulfur fuels from naturally occurring carbonaceous fuels.

Other objects and advantages of this invention will become more apparent from the following description and accompanying drawing which diagrammatically illustrates one embodiment of this invention.

In accordance with this invention the above objects and advantages are accomplished by dissolving substantially all of the potentially available fuel fractions of naturally occurring carbonaceous fuels, such as coal, lignite, peat, and the like, using a solvent derived from the original fuel feed stock under critically controlled conditions of temperature, pressure and atmosphere together with a very critical holding period in processing temperature, at which the normally insoluble portions of the fuel are decomposed, generally, by depolymerization of the feed fuel, to fractions soluble in the solvent. By observing the critical process parameters of this in vention, to be specified herein, these naturally occurring fuels are not only upgraded into novel low-ash, lowoxygen, low-sulfur fuels, but, in addition, this solution of the feed fuel is accompanied by a generation of additional quantities of solvent from a portion of the raw feed fuel which more than makes up any amount of solvent lost by mechanical losses thereof in the system.

More specifically, the drawing illustrates a continuous embodiment of this invention in which a raw feed fuel, such as Kentucky No. 11 coal which has been ground by a suitable means, such as a hammer mill (preferably the coal is finely ground to approximately percent through 200 mesh (US. Standard), is fed by means of a conveyor or the like to an agitated tank 1 where it is mixed with solvent (obtained from previous processing) at a ratio of about 1/1 to 4/1 solvent to coal. If desired, the coalsolvent slurry in tank 1 may be heated to any suitable temperature which will flash off any moisture which may be present in the coal.

Since the solvent used in this invention is derived from the coal being dissolved, its composition may vary, depending on the analysis of the coal being used as feedstock. In general, however, the solvent employed in this invention is a highly aromatic solvent obtained from previous processing of fuel, and will generally have a boiling range of about C. to 750 C., a density of about 1.1 and a carbon to hydrogen mole ratio in the range from about 1.0 to 0.9 to about 1.0 to 0.3. Generally, any good organic solvent for coal may be used as the initial start-up solvent in the process. A typical solvent is, for example, middle oil obtained from coal and having a boiling range of to 300 C. A solvent found particularly useful as a start-up solvent is anthracene oil or creosote oil having a boiling range of about 220 C.- 400 C. However, the selection of a specific start-up solvent is not particularly critical since during the process dissolved fractions of the raw feed fuel .form substantial quantities of additional solvent which when added to the solvent originally fed into the system provide a total amount of solvent which is greater than the original amount put in the process. Thus, regardless of what the original solvent may have been, it will lose its identity and approach the constitution of the solvent formed by solution and depolymerization of the raw fuel fed into the process. As a result the composition of the solvent approaches that of the same general composition as the de-ashed product of the processed feed fuel but of lower molecular weight, with the actual composition in each case determined by the composition of the particular raw feed fuel employed. For this reason the solvent, which is employed, may be broadly defined as that obtained from a previous extraction of raw carbonaceous fuels, in accordance with this invention.

In all events the ratio of solvent to coal in the slurry mixed in slurry tank 1 will be in the range of 0.6/1 to 4/ l with a preferred range of 1/ 1 to 2.3/1. Ratios of solvent to coal of less than 0.6/1 (i.e. 0.5/1) produce slurries which are of the consistencies of tar upon dissolution of the coal in the solvent, thus rendering them difficult to move in the system and which frequently cause clogging of the system. Ratios of solvent to coal greater than 4/1 may be used but provide no functional advantage in the solution process of this invention and sufferthe additional disadvantage of requiring additional energy or work for the subsequent separation of solvent from the deashed coal product for recycling in the system. As will be appreciated, the more solvent that is introduced into the system the more that must be recovered later on. So, from this standpoint, the lower the ratio that can be used, the better. However, other factors, either economic or those based on processability, may override this consideration and dictate that higher solvent to coal ratios be used. The viscosity of various solvent-coal slurries was measured at 75 C. to obtain clarification of the limits thereformed. It is believed that the following table clearly shows the significance of the 1/ 1 solvent to coal ratio of the slurry (i.e. 50% coal concentration) Viscosity of calSolvent slurry for various concentrations of coal at 75 C.

As can be seen in the above table, there is an increase in the viscosity of the coal-solvent slurry when the concentration of coal increases from 50 to 55 percent. This increase in viscosity causes higher pressure drops in moving the slurries through the system, and also greatly reduces the rate of filtration where employed in the system.

The slurry formed in tank 1 is then fed by means of any suitable method, for example a positive displacement pump 2, to a preheater 3 and then into a dissolver 4 which is suitably heated to maintain the slurry at its elevated temperature. It is essential in accordance with this invention, that hydrogen be added to the slurry ahead of the preheater 3 or dissolver 4 at a partial pressure of at least 500 p.s.i. The hydrogen employed is normally that recycled from previous processing together with any fresh make-up hydrogen required to provide the necessary hydrogen content. Although there is no critical upper limit to the hydrogen pressures employed, for practical reasons, the pressures employed will normally be in the range of 500 to 1500 p.s.i., with 1000 p.s.i. preferably employed.

The hydrogen pressurized fuel-solvent slurry is heated in the preheaters to rapidly raise the temperature thereof to about 370 C. to about 500 C., and preferably about 375 C. to about 440 C.

The tubes are sized, as to diameter and length, so as to enable the flow of slurry therethrough to be heated to operating temperatures as rapidly as is practical,

which in experiments has been obtained as low as 12 to 20 seconds. In general, the preheater will be designed to provide the desired rate of heating to the slurry at a heat flux of not greater than abOut 10,000 B.t.u./hour/sq. ft. of tube surface area. Normally in order to maintain good heat transfer, the diameter of the tubes will be sized so as to maintain the slurry in turbulent flow through the preheater.

The length of time in which the solution of the hydrogen pressurized slurry is continued in dissolver 4 is critical to the success of this process. Although the duration of treatment (solution) will vary for each particular carbonaceous fuel treated, it was found that the mechanics of the solution provide an accurate guide for the residence time of the slurry in dissolver 4. In this regard it was found that the viscosity of the solution obtained during processing of the slurry increases with time in dissolver 4, followed by a decrease in viscosity as this solubilizing of the slurry is continued and then followed by a subsequent increase in the viscosity of the solution on extended holding in the dissolver 4. One of the criterions used for determining the completion of the solution process, in accordance with this invention, is the relative viscosity of the solution formed which is the ratio of the viscosity of the solution to the viscosity of the solvent, as fed, to the process, both viscosities being measured at 210 F. Accordingly, the term Relative Viscosity as used herein and in the claims is restricted to and defined as the viscosity at 210 F. of the solution formed divided by the viscosity of the solvent at 210 F. fed to the system, i.e.,

Viscosity, it may be noted that as the solubilizing of the slurry proceeds, the Relative Viscosity of the solu- Relative Viscosity= tion first rises above a value of 20 to a point at which the solution is extremely viscous and in a gel-like condition. In fact, if low solvent to coal ratios are used, for example 0.5/ 1, the slurry would set up into a gel. After reaching the maximum Relative Viscosity, well above the value of 20, the Relative Viscosity begins to decrease to a minimum after which it again rises to higher values. It was found essential for the success of this invention that the solubilization be allowed to proceed until the decrease in Relative Viscosity (following the initial rise in Relative Viscosity) falls to a value of at least 10 and the resultant solution separated from undissolved residue of the coal before the Relative Viscosity again rises above 10. Normally, the decrease in Relative Viscosity will be allowed to proceed to a value less than 5 and preferably in the range of 1 /2 to 2.

It may be noted that, during the formation of the solution, the feed fuel depolymerizes in the presence of hydrogen to form fractions which are soluble in the solvent, and it was observed that the depolymerization of the coal during extraction is accompanied by the evolution of hydrogen sulfide, water, carbon dioxide, methane, propane, butane, and other higher hydrocarbons which will comprise part of the atmosphere in the dissolver 4.

It was found that the depolymerization, of the feed fuel, consumes hydrogen up to a Weight equivalent to about 2.0 percent of the weight of the feed fuel (as received), and under preferred conditions, in an amount of about 0.5 to 1 percent of the feed fuel.

Upon completion of the solubilization in dissolver 4, the resultant solution is then charged to a filter 5 for separation of the coal solution from undis'solved residue (i.e. mineral matter) of the feed fuel. The filter 5, as shown in the drawing, is a conventional rotary drum pressure'filter suitably adapted for pressure let down and venting of gases. It is to be understood that although a rotary drum filter has been described as being utilized in conjunction with this embodiment, other means of separation may be employed as for example centrifuges and the like.

The gases vented from filter are then passed through a line into a gas treating unit 6 in which hydrogen sulfide and carbon dioxide are scrubbed out in any suitable manner, as for example by caustic solutions. The remaining gas may be given any further treatment desired.

The hydrogen sulfide and carbon dioxide free gas recovered is then recycled to the process by feeding to fresh slurry being fed to preheater 3, with all make-up hydrogen being supplied by fresh hydrogen. Analysis of the recovered gases has shown that the over-all consumption of hydrogen throughout the system is quite low with the actual consumption of hydrogen being not greater than 2 percent (based on the feed fuel) and quite often as loW as 0.5 percent.

The filter cake or residue obtained in filter 5 is withdrawn therefrom for additional processing as desired, as for example solvent recovery, which will be discussed below. In practice further processing of the filter cake is desired since, in addition to mineral water, it may contain from between 40 to 50 percent, by weight, of solvent that can be recovered by pyrolytic distillation. Often this dried filter cake contains about 50 percent carbon and runs about 7,000 Btu. per pound. The further processing of the cake is particularly significant since the coal mineral matter and included solvent may comprise about 10 to percent of the total weight of the slurry fed to the system. Now where the filter cake is comprised of approximately to percent solvent, the amount of recoverable solvent comprises between about 5 to 15 percent of the original solvent fed into the system. As will be understood, if the filter cake is processed for the recovery of the solvent, the recovered solvent may be recycled into the system for the preparation of additional slurry for feeding into the system.

The filtrate from filter 5 is then pumped at a temperature of about 270 to 430 C. through suitable nozzles into a simple vacuum flash evaporator 7 for removal of the majority of the solvent. In accordance with conventional practice, the evaporator will be equipped with a demister to remove any entrained liquid in the vapor, and, also, suitable heaters will be located on the outside of the evaporator to make up for heat losses. The flashed solvent from the evaporator 7 may be passed to a still 8 or recycled directly to the system. The amount of solvent recovered for recycling to the system will generally comprise a quantity of about 85 to 100 percent of the amount of the solvent originally introduced into the system. This recycled solvent may all come from the evaporator or may be a mixture of solvent from the evaporator and solvent recovered from the filter cake processing. It is to be understood that solvent recovery may be accomplished by a variety of methods, such as wiped film evaporators, and thus such other means may also be employed if desired for recovery of solvent.

The remaining product from evaporator 7, which is liquid at this point may be used as such, or it may be pumped onto a continuous rotating steel belt 15 where it is cooled and solidified. This product, which solidifies upon cooling, is very brittle and breaks into flakes as it finally falls from the belt. Other methods may also be used to recover the product as for example spray cooling or prilling, or, again, if desired the product may be retained in the liquid state and used as such.

This resultant brittle product recovered from evaporator 7 is a hydrocarbon material which has little resemblance to the feed fuel charged into the system. As with the filter cake, a substantial amount of recoverable solvent remains in the product ranging from about 15 to about percent. The nature of this product is believed readily evident from the following properties thereof Density. gms./cc..

Btu/lb 6 which are set forth in conjunction properties of Kentucky No. 11 coal.

ANALYSIS OF PROCESS PRODUCT COMPARED WITH KENTUCKY N0. 11 COAL with corresponding Melting Point, C

As can be noted from the aboveanalysis, the percentage of carbon has increased, and the percentages of sulfur and oxygen are substantially lower.

The melting point of this product is influenced very strongly by the amount of volatile matter that is left in the product. For example, if a product having about 39 percent volatile matter and a softening point of 180 C. had been treated so as to leave therein approximately 50 percent volatile matter, its melting point would be down near 130 C.

The viscosity temperature curves of this product are very steep and allow fluidization and atomization into conventional firing systems using other fuels such as residual oils. It was found that upon heating the products of this invention to between 240 and 350 C. they become sufficiently fluid for various applications at these temperatures, i.e. fuels. The economics of the invention render the products of this invention competitive with residual oil and other fuels for many uses such as for gas turbine use, in applications such as in railroads, and the like.

The following examples will further and more specifically illustrate the nature of the invention and the manner in which the same may be carried out in practice, but it should be understood that the invention is not limited to the specific examples set forth below.

EXAMPLE I Kentucky No. 11 coal, having the same analysis given for it above, was dissolved in a solvent recovered from previous extraction runs (in accordance with this process) under the following conditions:

Process conditions:

Total gas pressure p.s.i.g 1,000 Hydrogen in gas percent Temperature C 410 Solvent/coal ratio 3/1 The coal/solvent slurry was heated within 12 to 20 seconds to the reaction temperature of approximately 410 C. and dissolution continued until the Relative Viscosity resultant of the solution rose and then dropped to 3.43. Thereafter, the solution was filtered at this Rela tive Viscosity from the undissolved residue of the coal; followed by treatment of the filtrate to separate recycle solvent from the product. The resultant product had the following analysis:

'7 EXAMPLE n In this example Kentucky No. 11 coal was again dissolved using a solvent obtained from previous extraction runs (in accordance with this process) under the following conditions.

Process conditions:

Total ,gas pressure p.s.i.g 1,000 Hydrogen in gas percent 80 Temperature C 420 Solvent/coal ratio 2/1 The processing was the same as in Example I, but the dissolution continued until the Relative Viscosity of the resultant solution rose and then fell to 4.57. The solution was then filtered from the undissolved residue of the coal, and was followed by separation of the solvent from the product (of the filtration) to yield a product having the following properties:

The properties of the foregoing products of Examples I and II are tabulated below together with the corresponding properties of Kentucky No. 11 coal for purposes of comparison:

ANALYSIS OF EXAMPLE I AND II PRODUCTS COMPARED WITH STARTING COAL Kentucky Example I Example II No. 11

P rocluct Product Coal,

MAF

Ash, percent 0.48 O. 23 7. 33 Carbon, percent 88. 16 88. 9O 78. 45 Hydrogen, peicent 5. 23 5. 07 5.20 Nitro en, percent. 1. 54 18. 3 1. 10 Sulfur, percent. 1. 17 0. 94 3. 74 Oxygen, percent. 3. 42 3.03 11. 40 Volatile Matter, pc 33. 6 39. 35 42. 88 B.t.u. per pound 15, 768 15,973 13, 978 Density, gms./ec 1. 24 1. 26 1.33 Melting Point, C 220 180 In order to further compare the products of Example I with the original coal, 500 gram samples of each were coked in a laboratory retort to a finish temperature of about 750 C.

Data on the coking of the two samples are tabulated below:

Example I Kentucky No.

11 Goal Gms. Per- Gms. Percent cent Yield of liquid 163. 8 2. 57 101.5 20.30 Yield of coke 332. 6 66. 52 314.0 62.8

Accountability 496. 4 99. 27 415. 83. 1 Gas plus losses 84. 5 17 Analysis of coke produced:

Carbon, percent 93. 59 82. 88 Hydrogen, percent 1. 24 0. 77 Sulfur, percent- 1. 24 2. 30 Ash, percent 2. 40 13. 20 Volatile Matter, percent- 2. 37 1.94 B.t.u. per pound 13, 965 12,563

Although the invention has been described with reference to specific materials, embodiments and details, various modifications and changes, Within the scope of the invention, will be apparent to one skilled in the art and are contemplated to be embraced within the invention.

What is claimed is:

1. In a process for preparing an upgraded, substantially ash-free and low-sulfur fuel from carbonaceous fuels which comprises:

(a) Preparing a slurry .of an organic solvent and a finely divided carbonaceous fuel in a ratio of about 1/1 to about 4/1 with said solvent being highly aromatic and having a boiling range of about 150 C. to about 750 C., a density of about 1.1 and a carbon to hydrogen mole ratio from about 1.0 to 0.9 to about 1.0 to 0.4;

(b) Feeding said slurry to a heating zone;

(0) Heating said slurry in said heating zone to a temperature in the range of about 370 C. to about 500 C.;

(d) Charging the slurry at said temperature to a solubilizing zone;

(e) Holding the charge of step (d) in said solubilizing zone;

(f) Separating the solution formed in the solubilizing zone from the residue of said fuel;

(g) Recovering at least a major portion of solvent having a boiling point in the range of 150 to 750 C. from said solution; and

(h) Returning the recovered solvent to the process for further processing of fresh carbonaceous fuels;

the improvement comprising:

adding hydrogen before the slurry is charged to the solubilizing zone to increase the pressure of the said slurry and hydrogen mixture to at least 500 p.s.i.;

holding the hydrogen pressurized slurry in said solubilizing zone at a pressure of at least 500 p.s.i. until the relative viscosity of the said hydrogen pressurized slurry rises substantially above 20 and then decreases below 10; and

then separating the solution formed in the solubilizing zone from the residue of the said fuel while the relative viscosity of the said solution is below 10.

2. The process of claim 1 wherein said carbonaceous fuel is bituminous coal.

3. The process of claim 1 wherein said carbonaceous fuel is lignite.

4. The process of claim 1 wherein said solvent is a solvent obtained from a previous processing of coal in accordance with said process.

5. The process of claim 1 wherein (a) The said holding of said slurry at said temperature is continued until the total solvent therein having a boiling point in the range of 150 C.750 C. is increased by dissolved portions of said fuel to an amount at least 130% of the original amount of solvent introduced into said process, and wherein (b) The said recovered solvent comprises an amount at least of the amount of solvent originally introduced in said process.

'6. The process of claim 5 wherein said carbonaceous fuel is bituminous coal.

7. The process of claim 5 wherein said carbonaceous fuel is lignite.

8. The process of claim 6 wherein said solvent is a solvent obtained from a previous processing of coal in accordance with said process.

9. The process of claim 1 wherein the said holding of said heated slurry at said temperature is continued until the relative viscosity thereof decreases to at least a value of 4, and separating the resultant solution from undissolved mineral matter while the relative viscosity of the said solution is not greater than 4.

10. The process of claim 9 wherein said carbonaceous fuel is bituminous coal.

11. The process of claim 9 wherein said carbonaceous fuel is lignite.

12. The process of claim 11 wherein said solvent is a solvent obtained from a previous processing of coal in accordance with said process.

13. The process of claim 9 wherein (a) Said carbonaceous fuel is bituminous coal,

(b) Said solvent is a solvent obtained from a previous solution of coal in accordance with said process,

(c) The said holding of said slurry at said temperature is continued until the total solvent therein having a boiling point in the range of 150 C.750 C. is increased, by dissolved portions of said fuel, to an amount at least 130% of the original amount of sol vent introduced into said process, and

(d) The said recovered solvent comprises at least 90% of the amount of solvent fed into said process.

14. The process of :claim 1 wherein the said holding of said heated slurry at said temperature is continued until the relative viscosity is decreased to a range of about 1 /2 to about 2, and separating the resultant solution from undissolved mineral matter while the relative viscosity of said treated slurry is in the range of about 1 /2 to about 2.

15. The process of claim 14 wherein said carbonaceous fuel is lignite.

16. The process of claim 15 wherein said solvent is a solvent obtained from a previous processing of coal in accordance with said process.

17. A process for preparing a substantially ash-free and low-sulfur fuel from coal which comprises the steps of:

(a) Feeding a slurry of finely divided coal and an organic solvent having a boiling point in the range of 150 C.750 C. to an elongated treating zone and as said slurry advances through said elongated zone;

(b) Raising the temperature of said slurry until the temperature reaches 375 C.440 C.;

() Adding hydrogen at a pressure of at least 500' p.s.i. to the slurry before it reaches its maximum temperature;

(d) Maintaining said slurry at said elevated temperature and under hydrogen pressure until (1) the relative viscosity of said slurry increases to at least 10, and (2) thereafter decreases to less than (e) Removing said treated slurry from said treating zone before its relative viscosity again increases to a value of greater than 10;

(f) Separating the resultant solution from undissolved residue of said coal;

(g) Recovering at least a major portion of said solvent from said solution; and

(h) Returning recovered solvent to the process for further processing of coal therein.

18. A process for preparing a solid substantially ashfree, low-sulfur fuel from coal comprising the steps of:

(a) Forming a slurry of an organic solvent and a finely divided coal;

(b) Providing in said slurry a hydrogen atmosphere under a pressure of at least 500 p.s.i. for said slurry with said solvent being highly aromatic and having a boiling point in the range of 150750 C., a density of about 1.1 and a carbon to hydrogen mole ratio from about 1.0 to 0.9 up to about 1.0 to 0.4;

(c) Raising the temperature of said hydrogen pressurized slurry to a temperature of about 370 C. to about 500 C.;

(d) Maintaining said hydrogen pressurized slurry at said temperature until the relative viscosity of the resultant solution rises above 20 and is followed by a fall below 10;

(e) Filtering said solution while its relative viscosity is below 10 to separate solution from undissolved residue of said coal;

(f) Recovering solvent having a boiling point in the 10 range of 150 C.-750 C. from the filtrate of step (e); and

(g) Cooling the remaining filtrate of step (f) to recover the said solid fuel thereby.

19. A process for preparing a substantially ash-free,

lowsulfur fuel from coal comprising the steps of:

(a) Heating under a hydrogen atmosphere of at least 500 p.s.i. a mixture comprised of a finely divided coal and an organic solvent having a boiling point in the range of l50-750 C. to a temperature in the range of 370500 C.;

(b) Holding said mixture under said atmosphere at said temperature until the relative viscosity of said mixture first rises above 20 and then falls below 10;

(c) Separating the resultant solution from undissolved residue 'of said coal while the relative viscosity of the said solution is below 10; and

(d) Recovering solvent having a boiling point in the range of ISO-750 C. from said solution.

20. A continuous process for preparing substantially ash-free, low-sulphur fuel which comprises the steps:

(a) Slurrying finely divided coal with a hydrocarbon solvent obtained from substep (i) below having a boiling point in the range extending from about 150 C. to about 750 C., said slurry being prepared to contain to 400 parts of solvent per 100 parts of coal;

(b) Continuously heating the slurry from Step (a) in a dissolving zone in which the slurry is heated to a temperature in the range of 370 C. to about 500 C.;

(c) Continuously feeding gas to the dissolving zone to maintain a gas pressure of 500 to 2,000 p.s.i. in the dissolving zone, said gas consisting of at least about 70 vol. percent hydrogen and the balance being substantilly hydrocarbon gases;

((1) Continuously withdrawing a liquid stream and associated gases from the dissolving zone;

(e) Continuously recovering the associated gases from the liquid stream of step (d);

(f) Removing hydrogen sulfide and carbon dioxide from said recovered gas;

(g) Recycling a portion of said hydrogen sulfide and carbon dioxide free gas to step (c);

(h) Continuously filtering the liquid stream from step (d) to remove mineral matter and any undissolved coal; and

(i) Continuously removing solvent fractions having boiling points falling in the range of C. to about 750 C. from the filtrate of step (h) and recycling said solvent fractions to step (a),

the residence time of the coal in the dissolving zone, the temperature in the dissolving zone and the gas pressure in the dissolving zone being maintained so that the liquid stream withdrawn from the dissolving zone in step (d) has a relative viscosity of 1 /2 to 10.

References Cited UNITED STATES PATENTS 2,476,999 7/ 1949 Orchin 208--8 2,686,152 8/ 1954 Franke 2088 2,913,388 11/1959 Howell et a1. 2088 3,143,489 8/1964 Gorin 2088 3,240,566 3/1966 Bullough et al 2088 

1. IN A PROCESS FOR PREPARING AN UPGRADED, SUBSTANTIALLY ASH-FREE AND LOW-SULFUR FUEL FROM CARBONACEOUS FUELS WHICH COMPRISES: (A) PREPARING A SLURRY OF AN ORGANIC SOLVENT AND A FINELY DIVIDED CARBONACEOUS FUEL IN A RATION OF ABOUT 1/1 TO ABOUT 4/1 WITH SAID SOLVENT BEING HIGHLY AROMATIC AND HAVING A BOILING RANGE OF ABOUT 150*C. TO ABOUT 750*C., A DENSITY OF ABOUT 1.1 AND A CARBON TO HYDROGEN MOLE RATIO FROM ABOUT 1.0 TO 0.9 TO ABOUT 1.0 TO 0.4; (B) FEEDING SAID SLURRY TO A HEATING ZONE; (C) HEATING SAID SLURRY IN SAID HEATING ZONE TO A TEMPERATURE IN THE RANGE OF ABOUT 370*C. TO ABOUT 500* C.; (D) CHARGING THE SLURRY AT SAID TEMPERATURE TO A SOLUBILIZING ZONE; (E) HOLDING THE CHARGE OF STEP (D) IN SAID SOLUBILIZING ZONE; (F) SEPARATING THE SOLUTION FORMED IN THE SOLUBILIZING ZONE FROM THE RESIDUE OF SAID FUEL; (G) RECOVERING AT LEAST A MAJOR PORTION OF SOLVENT HAVING A BOILING POINT IN THE RANGE OF 150* TO 750*C. FROM SAID SOLUTION; AND (H) RETURNING THE RECOVEERED SOLVENT TO THE PROCESS FOR FURTHER PROCESSING OF FURESH CARBONACEOUS FUELS; THE IMPROVEMENT COMPRISING; ADDING HYDROGEN BEFORE THE SLURRY IS CHARGED TO THE SOLUBILIZING ZONE TO INCREASE THE PRESSURE OF THE SAID SLURRY AND HYDROGEN MIXTURE TO AT LEAST 500 P.S.I.; HOLDING THE HYDROGEN PRESSURIZED SLURRY IN SAID SOLUBILIZING ZONE AT A PRESSURE OF AT LEAST 500 P.S.I. UNTIL THE RELATIVE VISCOSITY OF THE SAID HYDROGEN PRESSURIZED SLURRY RISES SUBSTANTIALLY ABOVE 20 AND THEN DECREASES BELOW 10; AND THEN SEPARATING THE SOLUTION FORMED IN THE SOLUBILIZING ZONE FROM THE RESIDUE OF SAID FUEL WHILE THE RELATIVE VISCOSITY OF THE SAID SOLUTION IS BELOW
 10. 